The tilt of the velocity ellipsoid measured at \(R<9\,\mathrm {kpc}\)  is basically consistent with the classical relation case that the \(\alpha _{\rm {tilt}}\)  is nearly antisymmetric about the plane, which was uncovered with various populations in the solar neighborhood (e.g. [1]}; [2]}; [3]}; [4]}). The \(\alpha _{\rm {tilt}}\)  measured between \(R=5\)  and 9 kpc confirms the findings of [5]} that the orientation of the velocity ellipsoid is more aligned with spherical when we move closer to the GC. In order to compare the velocity ellipsoid orientation above and below the plane, we estimate the gradients of \(\alpha _{\rm {tilt}}\)  with respect to \(\arctan (Z/R)\)  at \(Z>0\)  and \(Z<0\)  separately. We found a gradient of \(0.803\pm 0.026\) , \(0.784\pm 0.019\)  and \(0.718\pm 0.033\)  at \(5<R<7\,\mathrm {kpc}\) , \(7<R<8\,\mathrm {kpc}\)  and \(8<R<9\,\mathrm {kpc}\)  respectively for the north disk, as well as \(0.852\pm 0.078\) , \(0.802\pm 0.066\)  and \(0.321\pm 0.075\)  respectively for the south, suggesting that the flattening effect of the tilt along the Galactocentric radius is stronger in the south disk than in the north. The difference in the orientation between north and south disks is more pronounced in the Galactic anticenter. At \(R>9\,\mathrm {kpc}\) , when we move from \(|Z|\lesssim 1\,\mathrm {kpc}\)  to higher north disk, the orientation of the velocity ellipsoid stays between a horizontal one and a spherical one. The reversed tilt observed at \(Z<-1\,\mathrm {kpc}\) , evidenced by populations with different \(\rm {[Fe/H]}\) , indicates that the shapes of gravitational potential for the north and south parts of the outer disk are different when we move far away from the plane.
